Flexible brush



FIG. 1 is a front perspective view of a flexible brush which embodies the design;

FIG. 2 is a rear perspective view thereof;

FIG. 3 is a front view thereof;

FIG. 4 is a rear view thereof;

FIG. 5 is a right side view thereof; the left side view thereof being a mirror image of the right side view thereof;

FIG. 6 is a top view thereof; and,

FIG. 7 is a bottom thereof.

The broken-line showing of bristle tufts illustrate portions of the brush that form no part of the claimed design. 

The ornamental design for a flexible brush, as shown and described. 